Charles P. Daly

Some people held the earth to be hemispherical, and to be supported like a boat turned upside down upon the heads of four elephants, which stood on the back of an immense tortoise. Other primitive ideas represented the earth as a vast plain or flat island, surrounded on all sides by an inaccessible and interminable ocean. At the extremities and around the borders were placed the "fortunate isles, " or imaginary regions, peopled by giants, pygmies, and extraordinary beings.
The circumscribing water surrounding the irregular outlines of the land led to the idea of a universal ocean. But, when men began to have experience of the sea by early navigation, the idea of a circular horizon always observed led to the notion that the ocean was bounded, and the whole earth came to be represented as contained in a circle, beneath which were roots reaching downward...